The present invention relates to the field of fiber-reinforced composite materials, and in particular to methods and devices for manufacturing fiber preforms and finished composite products with complicated three-dimensional shapes.
Fiber-reinforced composite materials, referred to herein as composites, are materials comprised of fibers embedded in a matrix material. Typical fibers include but are not limited to glass fibers, carbon fibers (e.g. graphite fibers and/or more exotic forms of carbon, such as carbon nanotubes), ceramic fibers, and synthetic polymer fibers, such as aramid and ultra-high-molecular-weight polyethylene fibers. Typical matrix materials include but are not limited to thermosetting and thermoplastic polymers, such as epoxies, vinylesters, polyester thermosetting plastics, phenol formaldehyde resins, nylon, and PEEK; cement and concrete; metals; and ceramics.
Composite materials often combine high-strength and relatively light weight. In typical composite products, the fibers provide high tensile strength in one or more directions and the matrix material hold the fibers in a specific shape. A set of fibers roughly in the shape of a final product is referred to as a fiber preform. Typical prior fiber preforms are comprised of layers of fibers (often woven or bound into a sheet of fabric) that are cut and arranged into a desired shape. Because fibers and fabrics made from fibers only provide high strength in specific directions, multiple layers of fiber materials are often stacked in different orientations to provide strength and stiffness optimized for the intended usage of the final product.
Most prior composite manufacturing techniques require the production of a mold, mandrel, plug, or other rigid structure in the shape of the desired preform. Sheets of fiber fabric are then cut and arranged on this rigid structure. A matrix material, such as uncured polymer resin, may be embedded in the fiber fabric or applied to the fabric during or after the fabric layup process. The matrix material is then cured or hardened, often under elevated temperature and/or pressure differentials to ensure even distribution of the matrix material and prevent voids, air bubbles, or other internal defects. Pressure and/or temperature may be applied to the composite part during curing using techniques including but not limited to compression molding, vacuum bags, autoclaves, inflatable bladders, and/or curing ovens.
Unfortunately, prior techniques for manufacturing fiber preforms and final composite parts, especially for complex part shapes, are time-consuming and difficult to automate. For example, the cutting and/or arranging fabric in the mold or other rigid structure is often performed by hand, due to the difficulty in draping fabric over complex forms without wrinkles or other surface defects. As a result, composite products are much more expensive than equivalent products made using conventional materials.
Conventional fiber material pinning techniques take a stack of fiber material layers and impress pins through the stack by piercing the layers of the stack with pins, and then securing the pins. Such conventional pinning technique is analogous to stapling material layers together. One method called Z-pinning is a technique that inserts rigid reinforcements, such as metal pins or cured composite rods, (also called Z-pins or Z-fibers) perpendicular to the planes of the fabric layers of an uncured composite preform. Unfortunately, such conventional pinning techniques damage the material fabric when the pins pierce the fiber material layers and are limited to a fixed number of fabric layers and a relatively uniform distribution of Z-pins.
A further understanding of the nature and the advantages of particular embodiments disclosed herein may be realized by reference of the remaining portions of the specification and the attached drawings.